As the question implies, I wish to deform my mesh permanently with armatures and weight painting so that the changes I made in pose mode are reflected in edit mode.
You can deform the mesh permanently by applying the Armature modifier on the mesh object.
If you want to retain the non-deformed version, you can duplicate with Shift+D, hide the original as a backup (H), then apply the modifier. It's handy to make a "trash" collection for cases like this; You can use the M key instead to send backup objects to the hidden collection in case you ever need them again.
It's also possible to edit the deformed mesh while posed without applying the modifier, by selecting "Display modifier in Edit mode" and "Adjust edit cage to modifier result" in the Armature modifier's options.
Lastly, you can apply the armature modifier as a Shape Key, couple options to try and see what works best for your task.